FIG. 17 is a perspective view of a general drum continuous casting apparatus.
According to this apparatus, molten metal 3 is supplied to a pouring basin formed by a pair of cooling drums 1, 1, rotating in opposite directions (directions of arrows in the drawing), and side gates 2, 2, and is brought into contact with the surfaces of the cooling drums 1, 1 to form a solidified shell, casting a thin strip cast piece (metal sheet) 4.
FIG. 18 is an enlarged sectional view taken on line D—D of FIG. 17, showing a sliding portion of the side gate in sliding contact with end portions of the cooling drums at a kissing point at which the surfaces of the pair of cooling drums become closest to each other.
End surfaces 1a, 1a of the pair of cooling drums 1, 1 move in sliding contact with a ceramic plate 5 mounted on the side gate 2, and edge portions 1b, 1b of the surfaces of the pair of cooling drums 1, 1 seal up the molten metal 3, thereby preventing the molten metal 3 from leaking to the outside of the pouring basin. At this time, the end surfaces 1a, 1a of the pair of cooling drums 1, 1 have to be free from relative displacement in the axial direction (the drum axis direction) with respect to each other, and have to contact the ceramic plate 5 on planes.
The conventional internal structures of the above-described cooling drum 1 are shown in FIGS. 19 to 21.
Each of the cooling drums 1 has a structure in which an outer drum sleeve 10 of a copper (Cu) alloy is supported, from inside, by a drum body (core member) 11 of steel (SUS) in order to increase the rigidity of the cooling drum 1. Hollow shaft portions 11a are integrally assembled to opposite end portions of the drum body 11. Arrows in FIGS. 19 to 21 indicate the flow of cooling water.
The cooling drum shown in FIG. 19 was proposed by the present applicant in Japanese Patent Application No. 1986-66897. It is composed of the drum body 11, the drum sleeve 10 detachably fitted on an outer peripheral portion of the drum body 11, a pair of wedge rings 12A, 12B inserted in joining end portions of the drum sleeve 10 and the drum body 11 to fix the drum sleeve 10 and the drum body 11, and hold-down rings 13 fastened to opposite end surfaces of the drum body 11 to hold down one of the wedge rings, 12B.
FIG. 20 also shows a structure in which the drum sleeve 10 is supported by the drum body 11 located inwardly, and bonding end portions of the drum sleeve 10 and the drum body 11 are joined together by fillet welding 14.
FIG. 21 also shows a structure in which the drum sleeve 10 is supported by the drum body 11 located inwardly, and entire contact surfaces of the drum sleeve 10 and the drum body 11 are joined together by shrink fit 15.
In the cooling drum shown in FIG. 19, however, the axial elongation of the drum sleeve 10 due to thermal deformation (heat load) during casting cannot be restrained merely by the frictional force of the wedge rings 12A, 12B to prevent slippage. As a result, the drum sleeve elongates in the axial direction, and there is no guarantee that its elongation is axially symmetrical with respect to the drum center. Accordingly, a displacement in the axial direction occurs between the end portions of the pair of cooling drums 1, 1, posing the problem that sealing of molten metal between the cooling drums and the side gates 2 is insufficient.
In the cooling drum shown in FIG. 20, the sites of the fillet welding 14 restraining the elongation of the drum sleeve 10 are low in durability, and once either weld zone is destroyed, the drum sleeve 10 does not elongate axially symmetrically with respect to the center. Accordingly, a displacement in the axial direction occurs between the end portions of the pair of cooling drums 1, 1, posing the problem that sealing of molten metal between the cooling drums and the side gates 2 is insufficient.
In the cooling drum shown in FIG. 21, the entire surface of the joining portions of the drum sleeve 10 and the drum body 11 can be clamped. However, even if clamping can be performed most tightly within an elastic deformation of the drum sleeve 10, the elongation force of the drum sleeve 10 during casting is stronger than the frictional force of the joining surfaces, so that slippage occurs at the fitting surfaces. Moreover, there is no guarantee that the drum sleeve 10 elongates axially symmetrically with respect to the center. Accordingly, a displacement in the axial direction occurs between the end portions of the pair of cooling drums 1, 1, posing the problem that sealing of molten metal between the cooling drums and the side gates 2 is insufficient.
Furthermore, a clamping force may be increased during the shrink fit or the clamping to increase sliding resistance, thereby preventing slippage at the fitting surfaces. In this case, there is a risk that the drum sleeve 10 made of the copper alloy will be torn into pieces. To prevent this risk, it was necessary to increase the thickness of the drum sleeve 10 made of the copper alloy.
Thus, it was difficult to introduce forging during the manufacturing process for the drum sleeve 10 made of the copper alloy, and great variations arose in quality. As a result, the surface layer of the drum sleeve 10 made of the copper alloy was rapidly damaged under heat load during casting, presenting the problem that the drum sleeve 10 made of the copper alloy had a short life.
Conventionally, temperature control of the drum body 11 was not performed, so that a drum crown (concave crown) greatly changed under heat load during casting. Thus, there was a problem that a cast piece having an appropriate convex crown (cast piece crown) was not producible.
The object of the present invention is to provide a twin-drum continuous casting apparatus and method which have means for preventing various adverse influences due to differences in thermal expansion of constituent members, thereby increasing the reliability of the apparatus, and improving the quality of casting.